1. Field of the Invention
The present invention relates to an image scanning apparatus and method for scanning an image on a reading medium such as a sheet of paper.
2. Description of the Related Art
Conventionally, a flat bed type image scanner has been widely used for reading/scanning an image on a surface of a reading medium such as a manuscript. This flat bed type image scanner normally has a contact glass arranged in a horizontal direction as medium placement means. Below this contact glass, there is provided an image scanning mechanism.
This image scanning mechanism includes, for example, an image sensor having a number of photo elements arranged in a main scanning direction and a support body for supporting the image sensor at a position parallel to the contact glass in such a manner that the image sensor can be moved in a sub scanning direction. In this flat bed type image scanner, the image on a reading medium placed on the contact glass can be scanned as a number of main scanning lines continuous in the sub scanning direction.
It should be noted that as such a flat bed type image scanner, there is a model in which the image sensor is fixed and a pair of scanning mirrors is moved in the sub scanning direction for scanning an image on a reading medium. Moreover, there is an image scanning apparatus in which the image sensor is fixed and the contact glass is moved in the sub scanning direction. Furthermore, there is an image scanning apparatus in which the image sensor is fixed and a manuscript as the reading medium is moved in the sub scanning direction by a sheet feed mechanism.
In the aforementioned image scanning apparatuses using the contact glass, the reading medium is placed with its image downward on the contact glass and a user cannot observe the image which is being scanned.
Moreover, in the model having a fixed image sensor, a reading medium is placed with its image upward on a sheet feeding mechanism and a user can observe the image which is being scanned. However, a jam may be caused in the sheet feeding mechanism when comparatively thin sheets of paper are set on the sheet feeding mechanism.
These problems are solved by image scanning apparatuses disclosed in Japanese Patent Applications No. 6-133079 and No. 6-294160. These image scanning apparatuses includes a table as medium arrangement means on which a reading medium is placed, and above this table, there is provided a scanner head supported by a support arm.
The scanner head has an image sensor, an image formation optical system, and a reflecting mirror which are built in the scanner head. The reflecting mirror is rotatably supported on a rotary shaft which is arranged in parallel to the main scanning direction. The reflecting mirror reflects an image light, i.e., a reflected light or transmitting light from the reading medium, into a predetermined direction which vertically intersects the main scanning direction.
This image sensor has one-dimensional structure consisting of a number of photo elements arranged in the main scan direction so as to read a main scan line consisting of a number of dots. Furthermore, reflecting mirror is rotated so that the main scan line reading position is shifted in the sub scan direction. Thus, a two-dimensional image is read/scanned by the number of main scan lines continuous in the sub scan direction.
In the image scanning apparatus having the aforementioned configuration, a reading medium is placed with its image facing upward on the table. That is, a user can observe the image while it is being scanned. Moreover, there is no need of feeding a reading medium by a feeding mechanism. Accordingly, there is no problem in reading an image on a very thin sheet of paper or on a page of a thick book.
In the aforementioned image scanning apparatus, there is a problem that the optical path length from the image to the image sensor fluctuates during the sub scanning carried out by the rotation of the reflecting mirror.
This fluctuation brings about a problem that the focusing position in the image formation optical is not matched with the light receiving position in the image sensor. This problem has been solved by utilizing an image formation optical system having an extremely large depth of field or an automatic focus mechanism for correcting the image formation position in the optical system.
However, an optical system having a large depth of field results in increase of the optical aberration and lowering of the input light quantity as well as a complicated structure of the optical system. Moreover, the automatic focus mechanism requires a data processing of a scanned image to drive the optical system. This also complicates the configuration of the optical system.
It is therefore an object of the present invention to provide an image scanning method and -apparatus employing a reflecting mirror rotation for the sub scanning and having a simplified configuration for qualified scanning.
The image scanning method according to the present invention comprises steps of: reflecting with a reflecting mirror an image light generated from an image of a medium arranged in a plane continuous in a main scan direction and in a sub scan direction, into a predetermined direction vertically intersecting the main scan direction; introducing the reflected image light to an image formation optical system so as to obtain an image formation at position of an image sensor consisting of a number of photo elements arranged in a direction parallel to the main scan direction; rotating the reflecting mirror pivotally supported by a rotary shaft parallel to the main scan direction so that a scan position of the image sensor on the medium is moved in the sub scan direction; and displacing at least one of the image sensor and the image formation optical system movably supported in a direction of an optical axis, in an interlocked state with the rotation of the reflecting mirror.
Consequently, an image light generated from an image on a scan medium is reflected by the reflecting mirror in a predetermined direction vertically intersecting the main scan direction so that an image is formed at a light receiving position of the image sensor via the image formation optical system. Thus, the image light is read as a one-dimensional main scan line by a number of photo elements of the image sensor. Here, the reflecting mirror is rotated so as to move the scan position of the image sensor in the sub scan direction on the scan medium. Accordingly, the two-dimensional image is scanned as a number of main scan lines continuous in the sub scan direction.
Simultaneously with this, at least one of the image formation optical system and the image sensor is displaced in an interlocked state with the rotation of the reflecting mirror, so that the image formation position of the image formation optical system is matched with the light receiving position of the image sensor even if the scan position on the scan medium is moved in the sub scan direction by the rotation of the reflecting mirror.
It should be noted that the term xe2x80x9cimage lightxe2x80x9d represents a light flux reflecting an image on a scan medium. For example, the image light may be a reflected light from the image on the scan medium or a light transmitting through the image on the scan medium. Moreover, the main scan direction represents a direction of the number of photo elements arranged in the image sensor. The sub scan direction represents a direction vertically intersecting the main scan direction projected onto the scan medium.
The image scanning apparatus according to the present invention comprises: medium placing means for placing a scan medium having on its surface an image to be scanned, on a flat plane continuous in a main scan direction and in a sub scan direction; a reflecting mirror for reflecting an image light generated from the image of the medium arranged by the medium setting means, into a predetermined direction vertically intersecting the main scan direction; an image formation optical system for image formation at a predetermined position from the reflected image light; an image sensor provided at the image formation position of this image formation optical system and consisting of a number of photo elements arranged in a direction parallel to the main scan direction; a drive source for generating a predetermined drive force; a mirror support mechanism having a rotary shaft for supporting the reflecting mirror so as to be rotatable in a direction parallel to the main scan direction; a mirror drive mechanism for rotating with the drive force of the drive source the reflecting mirror supported by the mirror support mechanism so that a scan position of the image sensor on the medium is moved in the sub scan direction; a member support mechanism for supporting at least one of the mage formation optical system and the image sensor so as to be displacable in a direction of an optical axis; and a position correction mechanism for displacing at least one of the image sensor and the image formation optical system movably supported in a direction of an optical axis, in an interlocked state with the rotation of the reflecting mirror.
Accordingly, a scan medium is placed on a plane continuous in the main scan direction and in the sub scan direction, and an image light generated from an image on the scan medium is reflected by the reflecting mirror into a predetermined direction vertically intersecting the main scan direction. The image light reflected is introduced into the image formation optical system so as to form an image at a predetermined position. This image light is read as a one-dimensional main scan line by a number of photo elements arranged in the main scan direction of the image sensor.
Here, the reflecting mirror supported on a rotary shaft parallel to the main scan direction by the mirror support mechanism is rotated by the mirror drive mechanism with a drive force from the drive source so that a scan position of the image sensor with respect to the image on the scan medium is moved in the sub scan direction. Accordingly, a two-dimensional image is entirely read as a number of main scan lines continuous in the sub scan direction.
Simultaneously with this, at least one of the image formation optical system and the image sensor is displaced in an interlocked state with rotation of the reflecting mirror, so that the image formation position of the image formation optical system is matched with the light receiving position of the image sensor even if the image scan position on the scan medium is moved in the sub scan direction by the rotation of the reflecting mirror.
According to another aspect of the present invention, the position correction mechanism displaces at least one of the image sensor and the image formation optical system so that an image formation position of the image formation optical system is matched with a light receiving position of the image sensor even if the reflecting mirror is rotated so that the scan position on the medium is moved in the sub scan direction.
Consequently, even if the reflecting mirror is rotated to move the image scan position on the scan medium in the sub scan direction, the position correction mechanism displaces at least one of the image formation optical system and the image sensor, so that the image formation position of the image formation optical system is matched with the light receiving position of the image sensor. Thus, the image formation accuracy is not changed even if the optical path length is changed by the scan position movement in the sub scan direction.
According to still another aspect of the present invention, the position correction mechanism comprises: a cam rotated by the drive source; and a cam follower axially supported so that it can make a reciprocal movement in an interlocked state with rotation of the cam so as to displace at least one of the image formation optical system and the image sensor.
Consequently, when the cam connected to the drive source is rotated, the cam follower displaces at least one of the image formation optical system and the image sensor and accordingly, for example, at least one of the image formation optical system and the image sensor interlocked with the rotation of the reflecting mirror changes movement speed in a non-linear way.
According to yet another aspect of the present invention, the image formation optical system comprises a single mono-focus lens, and the position correction mechanism displaces at least the image formation optical system. Consequently, the image formation optical system is displaced by the position correction mechanism without requiring any wiring. Thus, it is possible to correct the image formation position with a single optical component not requiring any wiring.
According to yet still another aspect of the present invention, the medium placing means is a table on which a scan medium having on its surface an image to be scanned is placed, the reflecting mirror, the image formation optical system, the image sensor, the drive source, the mirror support mechanism, the mirror drive mechanism, the member support mechanism, and the position correction mechanism are arranged in a single scanner head, and the scanner head is supported by a support arm so as to be positioned above the table.
Consequently, an image on the scan medium placed on the table is scanned by the scanner head supported by the support arm, not requiring feed of the scan medium using a sheet feed mechanism or the like, and enabling a user to observe the image.